Our integration approach (Fig. 1a), relies on butt coupling between DFB and TFLN waveguides.
This approach allows for an efficient injection of carriers through the active quantum well region, which is essential for envisioned high-power laser operation. First, TFLN devices are fabricated [1]}, [2]} on a 600 nm thick, X-cut LN device layer that is bonded onto a 4.7 \(\mu \) m layer of thermally grown SiO2 on top of Si substrate (NanoLN). The thickness of the buried oxide is chosen so that the optical mode-height of the flipped DFB laser waveguide (\(\sim \)  4.66 \(\mu \) m) and TFLN waveguide (\(\sim \)  5 \(\mu \) m) (Fig. 1b) are nearly matched. Mode height matching is later fine-tuned using gold deposition. The waveguide width is chosen to be 800 nm to ensure single mode operation. The waveguides are first defined using a negative-tone electron-beam resist (FOx-16, Dow Corning). The pattern is then transferred to TFLN by reactive ion etching using Ar+ to reach the slab height of 300-nm. We later deposit 800-nm of SiO2 using plasma enhanced chemical vapor deposition as a device cladding. At the coupling region, the waveguides are tapered out to 8.2 \(\mu \) m in width. This horn coupler geometry ensures maximal overlap with the optical mode produced by the 5-\(\mu \) m wide DFB laser, and features high tolerances to lateral misalignment, mode height misalignment and separation (gap) between DFB and TFLN waveguides (Fig. 1c).
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